The subject of the invention is a process for the production of grinding tools having a basic body carrying an abrasive coating which consists of super-abrasives, such as diamond grains or grains of cubic-crystalline boronitride arranged finely distributed in a bond.
In the industrial production technology, resin-bonded grinding wheels in particular are used for the grinding of tools and are equipped with hard and wear-resistant materials, such as, for example, hard metals or ceramic materials. In addition, resin-bonded grinding wheels are employed for the machining of high-alloy steels. For this purpose, the hard-material granulation of grinding wheels of this type consist of natural or synthetic diamond or cubic-crystalline boronitride as an abrasive. Usually duroplastic resins, such as phenol resins, are used as bonds of such super-abrasives in resin-bonded grinding wheels and also contain, in addition to the hard-material grains arranged finely distributed, so-called fillers which contributed to a stabilization of the plastic structure and its elasticity. Such fillers consist, for example, of Silicon carbide in different grain sizes. Melamine resins, polyamides, polyimides and polisulphones can also be employed as a bond.
For the production of grinding wheels or, in general, grinding tools by the use of materials of this kind, according to known processes the resins, fillers and super-abrasives are introduced as mixtures into press molds made of hardened steel and are pressed under high pressure and appropriate temperatures onto corresponding basic bodies or abrasive-carriers, in order to convert them into a hardened duroplastic state.
For this purpose, where phenol resins, melamine resins and similar resins are concerned, press temperatures of, for example, 180.degree.-200.degree. C. and pressures of 1,500-3,000 Newton/cm.sup.2 are adopted. In contrast, for polyimide resins, even higher temperatures, namely up to 350.degree. C., and higher press pressures, such as up to 4,000 Newton, are necessary.
This known method of producing grinding wheels involves a high outlay, in as much as it requires the use of hardened and ground press molds which, as a result of the wall friction with super-abrasives, undergo continuous wear during their use, so that they are suitable only for a small number of pressings. Another disadvantage is the need to provide a press mold which is adapted to the particular grinding-wheel dimension.
Peripheral grinding wheels with a coating depth of, for example, 2 mm and with a length of abrasive coating of several hundred millimeters cannot be produced from one piece by this known process, but have to be assembled from a plurality of individual grinding wheels. This presents the problem of connection at the seams which, as a rule, should be non-parallel in the circumferential direction, because otherwise, for example during the so-called plunge-cut grinding, visible grinding traces occur on the workpieces to be machined.
Finally, a drawback of the known processes is to be seen in that only a very small number of grinding wheels can be produced under a single press in one pressing operation.